to the genetic abnormality and the consequently altered environment, the developmental trajectory may be atypical. If we assume the innate modularity view, one would predict that language and general cognitive development in populations affected by genetic disorders follow a developmental trajectory that mirrors the one seen in typical development (Pinker, 1999), although one or more components of this system may be anomalous. If we assume the neuro‐constructivist view, then we would predict that a genetic abnormality inevitably affects the developmental pathway, such that development proceeds along an atypical trajectory.
Although it is well established that many genetic syndromes are associated with communication disorders, there is still a large number of disorders for which there is no information available. The six best‐known genetic syndromes as far as language and communication are concerned are: Down syndrome (DS), Williams syndrome (WS), Fragile‐X syndrome, Prader‐Willi syndrome, Cri‐du‐chat syndrome, and Noonan syndrome (Rondal, 2001). This chapter will focus on WS and DS because these syndromes have been particularly implicated in theoretical debates about the status of language within human cognition and also because they have informed debates on innate modularity and neuro‐constructivism.
5.2 Language and Communication in Williams Syndrome (WS)
WS is a rare genetic disorder which is typically found in 1 in 20,000–50,000 live births (Greenberg, 1990), although recent research has reported incidence of 1 in 7,500 (Stromme, Bjornstad, & Ramstad, 2002). It occurs due to a deletion of approximately 25 genes on chromosome 7. The deletion includes the gene ELN, which codes for the protein elastin (Lowery et al., 1995). WS is characterized by physical abnormalities, heart and renal problems, failure to thrive in infancy, a characteristic face morphology known as “elfin” face, and mild to moderate learning difficulties. The WS neurocognitive profile is often described as uneven. This is due to the fact that individuals with WS have moderate to severe learning difficulties, profound impairments in planning, problem‐solving and spatial cognition, but relative strengths in social cognition, linguistic abilities, face processing and auditory rote memory (Mervis, Morris, Bertrand, & Robinson, 1999). Although language abilities tend to improve with increasing chronological age, once individuals with WS reach adulthood, linguistic abilities show relatively little improvement over time (Howlin, Elison, Udwin, & Stinton, 2010). Recent studies also present evidence that structural expressive language skills develop more rapidly than receptive language skills, which may lead to more distinctive language profiles over time (Van Den Heuvel, Manders, Swillen, & Zink, 2016). Also, there is emerging evidence that speech disfluencies in individuals with WS may be a significant marker of language impairment (Rossi, Sampaio, Gonçalves, & Giacheti, 2011).
Some of the first, seminal studies investigating language in WS reported “intact” language, especially with regard to morpho‐syntactic abilities. A number of pioneering studies by Bellugi and colleagues argued that despite severe cognitive impairments, individuals with WS have superior syntactic abilities (Bellugi, Bihrle, Neville, & Doherty, 1992; Bellugi, Marks, Bihrle, & Sabo, 1988; Bellugi, Wong, & Jernigan, 1994). Bellugi and colleagues were the first to suggest that individuals with WS offered evidence that there are clear dissociations between language and other cognitive abilities in the human cognitive system. A number of studies followed in the same direction, presenting data supporting the view that individuals with WS show enhanced grammatical ability compared with lexical ability, and better performance in grammar over lexical semantics (Clahsen & Almazan, 1998, 2001; Clahsen & Temple, 2003; Ring & Clahsen, 2005). These studies have argued that WS offers evidence for dissociations within the linguistic system into a computational component (concerned with rule‐governed operations involved in passive constructions, past tense formation in English, binding) and a lexical component (vocabulary store). In their studies cited above, Clahsen and colleagues showed that individuals with WS perform better with regular grammatical inflections compared with irregular, which involved retrieving items from the lexicon.
The regular/irregular issue has attracted a lot of interest and debate because of the theoretical implications. A number of studies have shown that individuals with WS perform better on regular inflections than on irregular ones (Clahsen, Ring, & Temple, 2004; Pléh, Lukács, & Racsmány, 2003). Studies have also reported that individuals with WS may be significantly impaired on irregular forms compared with controls, but not on regular forms (Clahsen & Almazan, 1998; Penke & Krause, 2004; Zukowski, 2004). However, no study to date has reported that individuals with WS outperform mental‐age controls, either on regulars or irregulars. Furthermore, the results of studies that have employed a larger number of participants (such as Thomas et al., 2001) show no interaction between group and regularity. As pointed out by Brock (2007), all studies that have investigated the performance of individuals with WS on regular versus irregular inflections suffer from “ceiling” effects, in that most of the participants in all the studies perform at ceiling on regulars, which makes it impossible for any group differences on irregulars to be found.
A large body of research has provided evidence for impaired morpho‐syntactic abilities in individuals with WS (Joffe & Varlokosta, 2007; Karmiloff‐Smith, Brown, Grice, & Peterson, 2003; Karmiloff‐Smith et al., 1998; Mervis & Klein‐Tasman, 2000; Stojanovik, Perkins, & Howard, 2001, 2004; Thomas et al., 2001; Volterra, Caselli, Capirci, Tonucci, & Vicari, 2003). Some of these studies show that not only do the individuals with WS not have superior language abilities, but that their language abilities may be on a par with those of children with diagnosed language impairments. For example, Stojanovik et al. (2004) compared the performance of a group of participants with WS aged between 6 and 12 and a group of participants with specific language impairment (SLI) or developmental language disorder (DLD) on a range of receptive and expressive standardized verbal measures, including measures of morpho‐syntax, and found similar performance across the two groups on all standardized language measures. The children with WS were completely indistinguishable on measures of morpho‐syntax from children with clinically diagnosed language impairment. Difficulties with the understanding of different morphosyntactic structures were also reported by Joffe and Varlokosta (2007). The participants with WS in their study, with a mean chronological age of 8 years 9 months, performed significantly less well on standardized and non‐standardized measures of grammatical ability than younger typically developing controls. The children with WS in their study had difficulties with the understanding and production of more complex syntactic structures like wh‐questions, and with the comprehension of passives, and performed lower than nonverbal mental age‐matched controls. Further evidence of specific difficulties with passive contractions relative to verbal and nonverbal mental age, and specific difficulties with passives when the verbs are psychological verbs, comes from a study by Perovic and Wexler (2010).
Some evidence suggests that the older the individuals with WS, the better their language abilities. The seminal studies by Bellugi and colleagues (Bellugi et al., 1988, 1994) had adolescents in their studies. Jarrold, Baddeley, and Hewes (1998) also showed that the verbal advantage in individuals with WS becomes more prominent as they get older. More recent studies, such as Musolino, Chunyo, and Landau (2010), which argue that individuals with WS have acquired the same core aspects of the computational component of language as neurotypical individuals, also report data from adolescents and adults with WS.
Evidence from older children and adolescents with WS also shows that they are able to extract patterns in language in an artificial grammar learning (AGL) paradigm, but possibly by relying on exemplar‐based rather than rule‐based processing strategies when processing language‐like stimuli. AGL performance is related to a person’s ability to predict language input based on the semantic and statistical context (Conway, Bauernschmidt, Huang, & Pisoni, 2010). A recent study by Stojanovik et al. (2018) reported that although the participants with WS (aged between 6 and 18) were outperformed by typically developing controls, the differences between the groups disappeared when nonverbal mental abilities were taken into account. Furthermore, the individuals with WS seemed to rely more on sequence familiarity rather than grammaticality when accepting or rejecting test sequences, and were able to extract patterns from the artificial grammar stimuli only when the training stimuli were presented with prosody. Such a finding fits well within the hierarchical framework